A masquerading detection system is a system that performs person recognition using a photograph of a registered person or a face image displayed on a monitor, when the authentication is based on a face and a head, for example. Such a masquerading detection system and a masquerading detection method are disclosed in Patent Document 1, for example. Paragraph [0015] of the document discloses that the lighting environment is changed by using an illuminating lamp, and masquerading can be eliminated based on the degree of similarity between face images obtained in different lighting environments. Paragraph [0061] of the document discloses various images of a face taken from various directions are obtained in advance, and the face images taken from certain directions are registered as an “authentication dictionary”.
Paragraphs [0015] through [0021] of Patent Document 2 disclose that three-dimensional information about a user is generated with the use of user images and respective image obtaining angles, and is compared with the three-dimensional shape of the face of the person that is stored beforehand. In this manner, masquerading using a photograph is eliminated. It should be noted that Patent Document 3, Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3 will be described later.